In recent years, antibody based therapeutics have become important instruments in treating human disease. (Brekke, O. H.; Sandlie. I. Nat. Rev. Drug Discovery 2003, 2, 52-62.) Current antibody-based therapeutics function either by blocking the effector actions of pathological molecules, or by targeting specific epitopes on cell surfaces for immune-mediated destruction. However, these approaches suffer from certain limitations, including severe side effects, lack of oral bioavailability, and high cost. (Allen. T. M. Nat. Rev. Cancer 2002, 2, 750-763.) Thus, alternative methods are being sought that would still exploit the powerful cytolytic potential of antibodies already present in the human blood stream yet avoid many of these disadvantages.
Acquired Immune Deficiency Syndrome (AIDS) is a world-wide epidemic that has claimed many lives and severely debilitated many more through immune suppression. A great deal of effort has been directed toward the development of a vaccine for this disease, without success. The failure to develop an effective vaccine underscores the need for new prevention and treatment strategies toward this disease.
The human immune system is highly versatile in its ability to target and destroy foreign pathogens. HIV, however, is an elusive virus to the body's immune system which has evolved mechanisms both to evade and to destroy the immune response of human hosts in the process of causing AIDS. Researchers recently found that one of the shortfalls of the human immune system in combating HIV is also one the antibody's stronger point against other viruses; its structure.
An antibody is a Y-shaped molecule with two epitopes comprising antigen recognizing proteins on the two Y tips. These two epitopes allow the antibody to bind to two proteins on the antigen's surface, creating a stronger bond when compared to a one-epitope protein bond. Viruses have proteins extending from their viral coat, which are the proteins the antibodies bind to.
HIV has fewer proteins than normal viruses. The proteins are placed farther apart and this structural difference is believed responsible for the antibody's epitopes being unable to bind to two different HIV surface proteins (See Klein et al. “Examination of the contributions of size and avidity to the neutralization mechanisms of the anti-HIV antibodies b12 and 4E10” Proceedings of the National Academy of Sciences, 2009 Abstract).
HIV has also been shown to bind to a surface molecule known as the CD4 or T4 receptor, which is present on various cells susceptible to HIV infection, including T lymphocytes and macrophages. (See Shaw et al., Science 226, pp. 1165-1171 for a discussion of tropism of HTLV-III.)
A few methods for recruiting naturally occurring antibodies to cancer cells have appeared in the literature, but none are believed to have been explored directed to HIV (See Carlson, C.; Mowery, P.; Owen, R.; Dykhuizen, E. C.: Kiessling, L. ACS Chem. Biol. 2007, 2, 119-127; Owen. R.; Carlson, C; Xu, J.; Mowery, P.; Fasella, E.; Kiessling, L. ChemBioChem 2007, 8, 68-82; Popkov. M.: Gonzalez, E.; Sinha, S.; Barbas, C. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 4378-4383; Popkov, M.; Rader. C; Gonzalez, B.; Sinha. S.; Barbas, C. Intl. J. Cancer 2006, 119, 1194-1207; (25) Low, P.; Henne, W.; Doorneweerd, D. Acc. Chem. Res. 2008, 41, 120-129; Lu, Y.: You, F.; Vlahov, I.; Westrick. E.; Fan, M.; Low, P. S.; Leamon, C. P. Mol. Pharm. 2007, 4, 695-706. (27) Rader. C.; Sinha, S. C.; Popkov, M.; Lerner, R. A.; Barbas, C. F. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 5396-5400), bacteria (Bertozzi, C. R.; Bednarski, M. D. J. Am. Chem. Soc. 1992, 114, 5543-5546; Bertozzi, C. R.; Bednarski. M. D. J. Am. Chem. Soc. 1992. 114, 2242-2245; Li, J.: Zacharek, S.; Chen, X.; Wang, J. Q.: Zhang, W.; Janczuk, A.; Wang, P. G. Bioorg. Med. Chem. 1999, 7, 1549-1558; Krishnamurthy, V. M.; Quinton, L. J.; Estroff. L. A.; Metallo, S. J.; Isaacs, J. M.; Mizgerd, J. P; Whitesides, G. M. Biomaterials 2006, 27, 3663-3674), and viruses ((32) Shokat, K. M.; Schultz, P. G. J. Am. Chem. Soc. 1991, 113, 1861-1862; Naicker, K. P.: Li, H.; Heredia, A.; Song, H.; Wang, L. Org. Biomol. Chem. 2004, 2, 660-664; Perdomo, M. F.: Levi. M.; Ilberg, M. S.; Vahlne, A. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 6).
In the HIV realm, most approaches have relied upon protein- or peptide-based antibody targeting constructs. For example, Shokat and Schultz (Shokat, K. M.; Schultz, P. G. J. Am. Chem. Soc. 1991, 113, 1861-1862) first demonstrated that anti-DNP antibodies could be redirected to immobilized protein targets (gp120 and streptavidin) as a therapeutic strategy toward HIV. More recent work in this vein has employed peptide-R-Gal conjugates to target human anti-Gal antibodies to HIV-infected cells. (Naicker, K. P.: Li, H.; Heredia, A.; Song, H.; Wang, L. Org. Biomol. Chem. 2004, 2, 660-664; Perdomo, M. F.: Levi. M.; Ilberg, M. S.; Vahlne, A. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 6)
While these peptide conjugates were shown to be effective in killing Env-expressing cells, they were also found to exhibit some non specific cytotoxicity. Bertozzi, C. R.; Bednarski, M. D. J. Am. Chem. Soc. 1992, 114, 5543-5546.
The present work sought to address these deficiencies, by providing compositions for treating HIV infection which can improve the immune system's ability to respond to HIV infection. We have discovered one way to assist the body is to recruit existing antibodies to attack HIV. Specifically, we have developed bifunctional molecules (Corson. T. W.; Aberle, N.; Crews, C. M. ACS Chem. Biol. 2008, 3, 677-692) capable of which inhibit the pathogenic behavior of HIV through two distinct mechanisms: (1) by interfering with viral entry via antagonism of the interaction between the viral envelope protein gp120 and the human protein CD4, and (2) by recruiting anti-dinitrophenyl (“anti-DNP”) antibodies, a population of antibodies present in high concentrations in the human bloodstream, to the surface of the HIV virus and/or HIV-infected cells.
Antibodies recognizing the DNP epitope have been estimated to constitute 1% of circulating IgM and 0.8% of circulating IgG. See: (a) Karjalainen, K., Makela. O. Eur. J. Immunol. 1976, 6, 88-93. (b) Farah, F. S. Immunology 1973, 25, 217-226. The prevalence of anti-DNP antibodies has been estimated at between 18 and 90% of humans. See: (c) Ortega, E.; Kostovetzky. M.; Larralde, C. Mol. Immunol. 1984, 21, 883-888. (d) Jormalainen, S.; Makela. O. Eur. J. Immunol. 1971, 1, 471-478. Consequently, administration of a bifunctional molecule which can recruit these existing antibodies to attack HIV in a patient suffering from HIV infection may provide a basis for an effective treatment for the symptoms associated with HIV infection.